Answer:
The phrase “not of this world” is perhaps most well-known for being a Christian apparel company (http://www.notw.com/). But what exactly does it mean that Christians are “not of this world”? The phrase comes from John 18:36 where Jesus says that His kingdom is “not of this world.” As His followers, Christians are members of His kingdom which is “not of this world,” that is, heaven (Philippians 3:20). Yes, we are on earth for now, but our earthly lives are nothing but a vapor (James 4:14). But eternity, now that is a long time, and that is where a Christian’s focus should really be (1 Peter 5:10).

The things of this world, wars, famine, suffering, poverty, etc., impact Christians and non-Christians alike. By remembering that we are “not of this world,” remembering that these things are just for a little while, we can see them in a different light. We are still in this world but we are no longer of it (John 17:14). We are still surrounded by all the horrors and tragedy of this life, but this is not our life (Philippians 3:8-14). The knowledge that we are not of this world gives Christians hope even in the darkest times (1 Peter 1:6-9); hope that this will pass and at the end of it we will be in heaven with our God, face to face forever (Revelation 21:3-4). This cracked and broken place is not where we belong, and it is not where we will stay (1 Corinthians 3:12).

Christians are not of this world. We have been adopted as heirs of heaven by God Himself and that is our world, our citizenship (Titus 3:7). And in the meanwhile we wait (2 Corinthians 5:12), and we hope (Romans 5:5), and we do what we can to bring others into the “not of this world” relationship with Jesus Christ. But this world is not our home, and never will be.